This invention relates to an artificial kidney device and in particular an artificial kidney device for automatically maintaining an ultrafiltration pressure substantially constant.
By "an ultrafiltration pressure" is meant a difference between internal and external pressures applied to a dialysis membrane consisting of a semipermeable membrane which is provided within a dialyzer.
A variety of artificial kidney devices, for example, a coil-type one, kiil-type one or one utilizing hollow fibers has been known up to this date. These artificial kidney devices are adapted to send blood from the artery of a human being through a suitable means to a dialyzer where urea, nitrogen, sodium, potassium, water content etc., included in blood are separated through a semipermeable membrane. The blood passed through the dialyzer is returned to the vein of the human being. With the dialyzer, the water content should be eliminated, in an amount far greater than that of the other components, through the semipermeable membrane. In addition to osmotic pressure, therefore, an additional pressure is generally required for the dialysis operation. One method is to apply ultrafiltration pressure to a dialyzer in an attempt to eliminate more water content. Taking the strength etc. of the semipermeable membrane into consideration, the ultrafiltration pressure is generally desired to be maintained at a level of 200 mm Hg. If the ultrafiltration pressure is too high, there is a fear that blood will flow out due to a breakage of the semipermeable membrane. If, on the other hand, it is too low, a dialyzing effect is lowered, and water content is not sufficiently eliminated from blood. For the purpose of maintaining the ultrafiltration pressure at suitable level, a method employed in the prior art is to mount a pinch-cock at a midway of a tube extending from a dialyzer into a vein of a human being. An ultrafiltration pressure of, for example, 200 mm Hg can be provided by restricting the flow passage of the tube by means of the pinch-cock.
However, a very delicate operation of the pinch-cock is required in adjusting the ultrafiltration pressure. Any slight operation of the pinch-cock causes a greater change in the resistance of blood. To make the ultrafiltration pressure at a prescribed level, therefore, the adjustment of the pinch-cock is conducted gradually, i.e., by repeating the adjustment several times. It will take more than 2 minutes for ultrafiltration pressure to settle down to a prescribed level after one adjustment has been made. For this reason, more than 10 minutes will be required in adjusting the ultrafiltration pressure to a desired level. If no due care should be exercised during adjustment, there is a chance that blood will flow out due to a breakage of the dialysis membrane.
The ultrafiltration pressure is related not only to the extent to which the pinch-cock is closed but also to the operation of transporting means of blood from the artery of a human being into a dialyzer, for example, rotations of a pump. If, therefore, the pump is changed in the number of rotations to increase a flow of blood, the above-mentioned delicate adjustment will be required on each occasion.